Bug 2528444

Summary: CVE-2026-85534 libsoup3: libsoup: HTTP/2 client crash in on_data_source_read_callback when SETTINGS INITIAL_WINDOW_SIZE shrinks during deferred body read [fedora-all]
Product: [Fedora] Fedora Reporter: Ganesh <gnaik>
Component: libsoup3Assignee: Gwyn Ciesla <gwync>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: rawhideCC: gnome-sig, gwync, mcrha
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["51499dbe-28a9-4fbb-8350-e5a998e429de"]}
Fixed In Version: Doc Type: ---
Doc Text:
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 2528440    

Description Ganesh 2026-09-04 09:19:16 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

A flaw was found in libsoup. The HTTP/2 client request-body path for non-pollable GInputStream sources buffers an asynchronous read sized to the current flow-control window, then later copies that entire buffer into nghttp2's DATA callback buffer without clamping to the callback length. A malicious HTTP/2 server can send a SETTINGS frame that reduces SETTINGS_INITIAL_WINDOW_SIZE while that read is in flight, making the next DATA callback length smaller than the already-buffered byte count. The only check is a g_assert(), which aborts the client in typical builds. If assertions are compiled out, nghttp2 rejects a return value larger than the allowed length and fails the session.